High definition color television systems are known. Such systems provide a television picture image which is much higher in vertical and horizontal resolution than presently utilized standard television broadcasting systems such as NTSC, PAL (Phase Alternation by Line) and SECAM (Sequential Couleur a Memoire).
An example is the 1125/60 high definition television system proposed by NHK (Nippon Hoso Kyokai or Japan Broadcasting Corporation). This system is featured by having 1125 scanning lines, an aspect ratio of 16:9, and 2:1 interlace scanning, with a field frequency of 60 Hz. The luminance signal bandwidth is about 20 MHz, while the chrominance signal bandwidth is approximately 7.0 MHz.
A system for the transmission of such a high definition color television signal is disclosed in U.S. Pat. No. 4,745, 459 issued May 17, 1988, incorporated herein by reference. This system provides bandwidth reduction of the high definition video signal from approximately 26 MHz to 8.1 MHz. However, such a system cannot be used for terrestrial broadcast over single conventional transmission channels which are limited to 6 MHz in bandwidth. Even further, the high definition television signal of the type referred to is a time compressed and time division multiplexed signal in which luminance and chrominance signals are multiplexed in time to eliminate interference between the chrominance and luminance signals. Therefore, even if such a signal required a bandwidth less than 6 MHz, it could not be decoded and displayed on a conventional receiver such as an NTSC receiver, since the NTSC television signal is a composite signal in which a luminance signal is multiplexed with a color subcarrier which is itself modulated by a chrominance signal and the two signal formats are thus not compatible with each other.
In referring to high definition television systems proposed for use in the United States and where compatibility with the existing NTSC system is the object, it has become a practice to designate such systems as "channel compatible" and/or "receiver compatible". A channel compatible system is said to be one in which the high definition signal can be encoded and broadcast transmitted with the presently assigned 6 MHz bandwidth frequency channels of the NTSC system. A receiver compatible system is one in which the signal can be decoded by and displayed by a conventional NTSC television receiver.